In recent years, various health check chips have been developed. Most of these health check chips are card devices called “μ-TAS” (Micro Total Analysis System), which have miniature flow path parts. A miniaturized flow path is very useful in that the required amount of a sample to extract from a living organism is small. Further, when entire apparatus including the health check chip is made small by miniaturizing the flow path, the apparatus is applicable for use in POCT (Point of Care Test) that allows diagnosis in doctor's offices and households, not only in relatively large-scale hospitals.
In cases where a large amount of fluid flows, a pump is generally used as liquid transferring means. However, in a miniature flow path in which only a very small amount of fluid flows, it is not possible to disregard the influence of the dead volume generated in tubes connected with the pump. Therefore, a pump is generally not suitable for the liquid transfer means of for chips used in POCT.
Using centrifugal force for the source drive is one method of liquid transfer suitable for use in POCT (for example, Patent Documents 1 to 5). A method of liquid transfer using centrifugal force offers an advantage of not generating a dead volume and performing many processes at the same time in parallel.
For example, the substrate disclosed in Non-Patent Document 1 has a plurality of microchambers and micro-flow paths. In the substrate, the widths of the micro-flow paths connecting between the microchambers are adjusted each other. To be more specific, in a range between about 10 μm and 100 μm, micro-flow paths that are more distant from the center of rotation have a narrower width. By this means, a micro-flow path that is more distant from the axis of rotation generates greater capillary force. Liquid in the miniature chambers, the liquid transfer of which is prevented by the capillary force produced in the micro-flow paths, is transferred to the neighboring microchambers in the direction of centrifugal force by the centrifugal force produced by the rotation of the substrate. The centrifugal force required to transfer liquid in a microchamber matches the capillary force produced in a micro-flow path. As described above, a micro-flow path is designed to produce greater capillary force when the micro-flow path is placed more distant from the axis of rotation. Therefore, without increasing the speed of rotation, it is not possible to transfer liquid from one microchamber to a neighboring microchamber in the direction of centrifugal force. That results in realizing stepwise liquid transfer.    Patent Document 1: Japanese Patent Application Laid-Open No. 2000-065778    Patent Document 2: Japanese Translation of a PCT Application Laid-Open No. 2001-503854    Patent Document 3: Japanese Translation of a PCT Application Laid-Open No. 2002-503331    Patent Document 4: Japanese Patent No. 3356784    Patent Document 5: Japanese Patent No. 3469585    Non-Patent Document 1: Micro Total Analysis Systems 2000, pp. 311-314